Fine jewelry chains, in general, and fine jewelry rope chains, in particular, are well known. In U.S. Pat. Nos. 4,934,135 and 4,996,835, there are disclosed rope chains and methods for preparing such rope chains having reduced weight and labor costs compared with conventional rope chains of the same chain diameter. A rope chain of the prior art is illustrated in FIG. 1A.
In the field of rope chains there are known both solid rope chains and hollow rope chains. A solid rope chain is a rope chain whose links are made from solid portions of metal, while a hollow rope chain is a rope chain whose links are hollow. While the general appearance of a rope chain is not affected by the links thereof being either solid or hollow, the amount of precious metal used in a solid rope chain of a given size is significantly greater than the amount of precious metal used in a hollow rope chain of the same size. Accordingly, a hollow rope chain of a given size is significantly cheaper than a solid rope chain of the same size.
A particularly popular type of rope chain is a diamond cut rope chain. Such a chain comprises flat cuts or facets on the outer perimeter of at least some of the chain links to provide a chain with a high luster flat surface finish that reflects light and gives the chain a sparkle effect. Diamond cut facets are known to be formed on solid rope chains by cutting or shaving a flat facet from a curved section of the links.
Solid diamond cut rope chains have such flat facets generally cut about one third or more into the thickness of the chain link in order to obtain a reasonable size flat shiny surface. In this case, the amount of precious metal sheared away can be as much as 10% of the weight of the chain and although the metal shearings are collected and recycled, a significant amount of precious metal is nevertheless lost in the process.
Although it is known to form diamond cut facets on hollow rope chains, this presents certain problems due to the relative thinness of the outer wall of the hollow links used. In some cases the outer wall may be as thin as 0.05 mm. Accordingly, the forming of a facet in the way in which facets are formed on a solid rope chain would at least cause severe weakening of the outer wall of the link and would probably make a hole therein.
In U.S. Pat. No. 5,125,225 to Strobel, there is described the making of flat facet hollow rope chains. The method involves wrapping a hollow rope chain about a lathe drum, freezing the drum, applying water to the chain to freeze it in place thereby immobilizing it, and applying, by means of a burnishing tool, a plurality of incremental deformative thrusts of blunt force against some of the curved outer wall portions of the hollow links until this outer wall is deformed and pushed back towards the inner wall of the links, thus flattening portions of the curved outer wall.
The flattened portions of the outer walls are then diamond cut to remove or shave off a very thin layer of metal (about 0.001 to 0.002 mm) to provide smooth and shiny flat facets without making a hole in the link. The cross-section of the faceted area is deformed relative to the cross-section of the rest of the chain link.
A disadvantage of the above-described method to Strobel is that as only a very thin layer of metal is shaved from the flattened portions, any substantial dents introduced into the surface by the thrusts of the burnishing tool will remain even after diamond cutting of the facets. Accordingly, great control is required in the flattening of the portions whereat facets are to be formed.
While hollow rope chains have the advantage of being lightweight, and, therefore, less expensive than their solid counterparts, the strength of the individual links is considerably less than that of similar-sized solid links. It will also be appreciated that the cutting into the wall of a conventional hollow link causes yet further weakening of the link and, accordingly, of the chain.